Reciprocating-piston drive mechanism

ABSTRACT

A reciprocating-piston drive mechanism comprises a reciprocating-piston assembly defining a spherical socket and including a piston body. A connecting rod is arranged for pivoting movement in a plane and has a ball head fitted in the spherical socket. A coupling between the ball head and the piston assembly is arranged to transform the pivoting movement of the connecting rod and ball head into a reciprocating rotation of the piston body about its axis. The coupling includes a first coupling member attached to, and non-rotatable relative to, the piston body, and a second coupling member attached to, and carried by, the ball head, the second coupling member engaging the first coupling member.

This is a continuation-in-part of our copending U.S. Pat. applicationSer. No. 887,502, filed Mar. 17, 1978 now abandoned.

The present invention relates to improvements in a reciprocating-pistondrive mechanism for an internal combustion engine. Known mechanisms ofthis type comprise a piston body having an axis and defining a sphericalsocket, piston ring means carried by the piston body, and a connectingrod arranged for angular movement and having a ball head fited in thespherical socket of the piston body. A coupling between the ball headand the piston body is arranged to transform the angular movement of theconnecting rod and ball head into a rotation of the piston body aboutthe axis thereof.

U.S. Pat. No. 3,500,724, whose disclosure is incorporated herein byreference, relates to a reciprocating-piston drive mechanism of thistype, wherein the coupling includes a coupling pin rotatably mounted inthe ball head and extending transversely to the plane in which theconnecting rod is angularly movable and at an oblique angle to the axisof the connecting rod. The coupling further includes a coupling memberhaving slot means extending parallel to the axis of the piston body andadapted to receive respective flattened ends of the coupling pin. Inthis mechanism, the coupling member is angularly oscillated about thelongitudinal axis of the piston body in response to the angular movementof the connecting rod. In order to ensure that the wear of the pistonbody is uniform and to decrease the total wear of the piston, it haspreviously been attempted to impart unidirectional rotation to thepiston body. For this reason, the coupling member and piston body havehad a slip connection or an overrunning clutch for rotation in only onedirection when the piston body is adjacent to one or the other of itsdead center positions. Such arrangements have the disadvantage that theelements of the overrunning clutch or unidirectional ratchet mechanismconnecting the coupling member and piston body involve an increasedstructural expenditure and add to the weight so that the mass forces areincreased. These increased mass forces result in an increase of thenormal force exerted on the sliding surface of the cylinder so that theload on the piston body and the stresses on the bearings are increasedas well as the noise which is generated. The rotation of the piston bodyonly in one direction requires that the piston body is axiallysymmetrical and for this reason cannot be provided in the piston headwith an unsymmetrical recess for combustion or for receiving the valvedisc, although such design would be desirable in heavy-duty engines.Finally, the spherical socket means have a relatively wide opening forthe access of the connecting rod because the opening must allow for theangular movement of the connecting rod in every rotational position ofthe piston body. Owing to this wide opening, the spherical socket has amuch smaller surface so that excessively high pressures per unit of areamay result.

It is an object of the invention to eliminate these disadvantages and toprovide a reciprocating-piston drive mechanism which is of the kinddescribed first hereinbefore and ensures that the structural expenditureis reduced as well as the weight of the piston body and which does notrequire an axially symmetrical design of the piston body.

This object is accomplished according to the invention with a couplingbetween the ball head and the piston assembly, which is arranged totransform the pivoting movement of the connecting rod and ball head intoa reciprocating rotation of the piston body about the axis thereof. Thecoupling includes a first coupling member attached to, and non-rotatablerelative to, the piston body and a second coupling member attached to,and carried by, the ball head, the second coupling member engaging thefirst coupling member.

The invention is based on the recognition that uniform and reduced wearcan be ensured even when the piston body is not unidirectionallyrotated, provided the piston rings are rotated only in one directon. Itfurther recognized that it requires no slip connected or otherunidirectional clutch between the piston rings and the piston totransform the reciprocating rotation of the piston due to itsnon-rotatable connection to the coupling member into a continuousunidirectional rotation of the piston rings. This is due to the factthat the piston rings are pressed against the side walls of the pistonring grooves housing them with different forces, due to the differencesin the gas and mass forces in the range of the upper and lower pistondead center positions, so that the frictional engagement of the pistonrings with the side walls of the grooves causes the rings to rotate withthe piston body in the range of the upper dead center position while, inthe lower dead center position, the friction between the piston ringsand the surrounding cylinder wall predominates and prevents a reverserotation of the piston rings. This results in the additional advantagethat the gas forces exerted on the piston rings lying one over the otherare not equal but decrease as the distance from the piston headincreases so that the rings are rotated through different angles and theslots of the piston rings are not disposed on the same generatrix of thecylinder for an excessively long time. Even when internal combustionengines operate under heavy load, the short time for which two or morepiston ring slots may be aligned in a direction which is parallel to thepiston axis is not sufficient for an occurrence of deleterious hotspots. Because the coupling member performing an angular oscillation isnon-rotatably connected to or forms part of the piston and no one-waycoupling is provided, the structural expenditure and the weight of thepiston are much decreased so that considerable advantages are afforded.Because the piston body oscillates only through an angle of a fewdegrees, the piston body may be nonsymmetrical with respect to its axisif, for example, the recesses for receiving the valve disc are enlargedto allow for that small angular movement. Finally, the ball head andspherical socket may even be offset from the axis of the piston body sothat the piston body is tilted. Such tilting is desirable to reducenoise and to equalize the stresses on the piston body.

The above and other objects, advantages and features of this inventionwill become more apparent from the following detailed description of anow preferred embodiment thereof, taken in conjunction with theaccompanying drawing wherein

FIG. 1 is a sectional view taken on line I--I in FIG. 3 through the axisof the piston body and shows those parts of a reciprocating-piston drivemechanism which are essential for the invention,

FIG. 2 is a sectional view taken on line II--II in FIG. 3 through theaxis of the piston body, and

FIG. 3 is a horizontal sectional view taken on line III--III in FIG. 2,the cylinder having been omitted.

Referring now to the drawing, the illustrated reciprocating-piston drivemechanism is shown to comprise a reciprocating-piston assembly defininga spherical socket and including piston body 2 having an axis anddefining upper part 6 of the socket. Piston ring means is carried by thepiston body and is shown to be comprised of a series of piston rings 4defining in piston grooves 5 housing them a clearance which is too smallto be represented in the drawing.

Connecting rod 8 is arranged for pivoting movement in a plane and hasball head 9 fitted in the spherical socket of piston assembly. As willbe described in more detail hereinafter, a coupling is arranged betweenball head 9 and piston assembly to transform the pivoting movement ofthe connecting rod and ball head, which is indicated by double-headedarrow 10 in FIG. 2, into a reciprocating rotation of piston body 2 aboutthe axis thereof. The coupling includes first coupling member 7, 7'attached to, and non-rotatable relative to, piston body 2 and secondcoupling member 13 attached to, and carried by, ball head 9. The secondcoupling member engages the first coupling member.

In the illustrated embodiment, first coupling member 7, 7' is part ofthe piston assembly and a lower part of the socket is defined by thefirst coupling member. The first coupling member has slot-like bore 16adjacent the socket and extending longitudinally in the plane whereinthe connecting rod is pivoted. As shown in FIG. 3, bore 16 is ofapproximately cardioid cross section in a plane transverse of thepivoting plane. This design may be adopted because piston body 2performs only a relatively small angular oscillation during thereciprocating rotation rather than a continuous unidirectional rotation.The use of a relatively narrow bore rather than a circular holepreviously required for accommodating the connecting rod results in anincrease of the bearing surface of the spherical socket so that thepressure per unit of area is decreased. The bearing surface of thespherical socket is increased further by imparting to slot-like bore 16a cardioid cross section in exact adaptation of the two motions of theconnecting rod and piston body. The longitudinal extension of bore 16and the direction of the angular pivoting movement of connecting rod 8are approximately the same.

Connecting rod 8 and bore 16 have a common axis in the plane in whichthe connecting rod is pivoted and first coupling member 7, 7' furtherhas coupling slot means shown to consist of two slots 15, 15. Two sidewalls extending transversely to the plane and parallel to the axis ofpiston body 2 define each slot 15 and each slot is open to the sphericalsocket, as clearly shown in FIG. 1 wherein one of the side walls of eachslot is seen in side view. In the illustrated embodiment, the firstcoupling member consists of two parts 7 and 7' defining joint Ttherebetween (see FIGS. 2 and 3) extending substantially in the plane inwhich connecting rod 8 is pivoted in the direction of arrow 10. Theangular pivoting movement is effected by the rotation of a crankshaft(not shown) to which connecting rod 8 is connected, this angularpivoting movement being indicated in phantom lines in FIG. 2. As shownin FIGS. 1 and 2, the illustrated coupling member 7, 7' has an end faceforming one end of the reciprocating-piston assembly and the assemblyincludes centering ring 11 disposed on the end face and engaging the twoparts 7 and 7' of the first coupling member for holding them together.Screws 12 extend parallel to the axis of piston body 2 and secure thecentering ring and the two coupling member parts to piston body 2.

While the two halves of the first coupling member could be welded orotherwise non-rotatably affixed to piston body 2, assembling them withthe centering ring and screws results in a structure which may bereadily assembled and taken apart and in which the centering ringbridges the clearance existing between the two coupling member parts andthe piston body.

Because a part of the spherical socket is defined by the first couplingmember, which thus performs a dual function, the structure is simple andmay easily be assembled. The two-part coupling member enables theconnecting rod to be fitted through the coupling member before thelatter is mounted on the piston body over the ball head. A connectingrod could be fitted through a one-part coupling member only if the bigend bearing of the connecting rod can be removed.

However, the coupling may have other designs. For instance, the firstcoupling member may be provided with a coupling pin and the ball head ofthe connecting rod may be provided with a slot for guiding the pin, orthe coupling pin may extend in the crank plane in a direction normal tothe axis of the connecting rod and the slot in the surrounding couplingmember may be oblique.

In the illustrated embodiment, the second coupling member consists ofcoupling pin 13 rotatably mounted in ball head 9 and extendingtransversely to the plane wherein connecting rod 8 is pivoted, at anoblique angle (see FIG. 1) to the axis of the connecting rod. Thecoupling pin has respective flattened ends 14, 14 received and fitted incoupling slots 15, 15 wherein the ends of the coupling pin hold itagainst rotation relative to the reciprocating-piston assembly. Thecoupling pin is mounted rotatably in a diametrical bore extendingthrough ball head 9. Accordingly, coupling pin 13 extends transverselyto the plane of the angular pivotal movement (arrow 10) of connectingrod 8 and the axis of the coupling pin passes through the center of ballhead 9.

Owing to this coupling arrangement, when the crankshaft is rotated topivot connecting rod 8 and ball head 9 in the direction of double-headedarrow 10, flattened ends 14 of coupling pin 13, which are keyed tocoupling slots 15 in the piston assembly, are similarly angularlyoscillated in opposite directions, each coupling pin end beingpositioned at opposite sides of the center of ball head 9. Looking atball head 9 along the axis of piston body 2, the angular oscillation offlattened coupling pin ends 14 is seen as a pivoting movement of theaxis of coupling pin 13 about the axis of piston body 2.

Since the coupling pin is thus keyed to the first coupling member 7, 7'and the latter is non-rotatable relative to piston body 2, this body isreciprocated according to the pivoting movement of the axis of thecoupling pin. In every position of the first coupling member, the twoside walls defining each coupling slot 15 are parallel to the axis ofpiston body 2. Therefore, coupling pin 13 must be rotatably mounted inthe diametrical bore of ball head 9 to ensure that flattened couplingpin ends 14 remain aligned with the side walls, i.e. parallel to theaxis of the piston body, regardless of the angular position ofconnecting rod 8 and coupling pin 3. If the coupling pin werenon-rotatable with respect to the ball head, the coupling pin ends wouldhave to be cylindrical to fit in coupling slots 15 in every position ofthe pivotally moving connecting rod and coupling pin.

As will be appreciated from the above description, pivoting ofconnecting rod 8 in the direction of double-headed arrow 10 in a plane,which is shown to pass through the axis of piston body 2, will causereciprocating rotation of the piston body about the axis.

What is claimed is:
 1. A reciprocating-piston drive mechanismcomprising(a) a reciprocating-piston assembly defining a sphericalsocket and including(1) a piston body having an axis and defining atleast part of the socket, and (2) piston ring means carried by thepiston body, (b) a connecting rod arranged for pivoting movement in aplane and having(1) a ball head fitted in the spherical socket of thepiston assembly, and (c) a coupling between the ball head and the pistonassembly, the coupling being arranged to transform the pivoting movementof the connecting rod and ball head into a reciprocating rotation of thepiston body about the axis thereof and the coupling including(1) a firstcoupling member attached to, and non-rotatable relative to the pistonbody, and forming part of the piston assembly, the first coupling memberconsisting of two parts defining a joint therebetween extendingsubstantially in the plane and has an end face forming one end of theassembly, the first coupling member defining a part of the socket andhaving a bore adjacent the socket and extending longitudinally in theplane, the connecting rod and the bore having a common axis in theplane, and the first coupling member further having a coupling slotmeans extending transversely to the plane and parallel to the axis ofthe piston body and the coupling slot means being open to the sphericalsocket, and (2) a coupling pin rotatably mounted in the ball head andextending transversely to the plane at an oblique angle to the axis ofthe connecting rod, the coupling pin having respective ends glidinglyreceived in the coupling slot means, (d) the assembly including acentering ring disposed on the end face and engaging the two parts ofthe first coupling member for holding them together, and screwsextending parallel to the axis of the piston body and securing thecentering ring and the two parts to the piston body.
 2. Thereciprocating-piston drive mechanism of claim 1, wherein the bore is ofapproximately cardioid cross section.